The famous Belgian detective, Hercule Poirot, thought he had an ace up his sleeve in Five Little Pigs when he waved a scented handkerchief to trigger memories in one of his suspects. Modern research suggests that he would have had a better chance of success if he had, in fact, done it while his target was in deep slumber.

The results of a controlled experiment, published in the journal Science last year, showed that the smell of roses-- delivered to people’s nostrils as they studied and, later, as they slept-- improved their performance on a memory test by about 13 percent. It is now only a matter of time before an entrepreneur exploits the commercial possibilities of this finding by promising struggling students the elixir of memorability.

Smell is said to be the most primitive of our senses, and olfactory senses follow a more direct path to the hippocampus, which is the brain's memory archive, compared to other sensory perceptions like sight and sound which are pre-processed by the thalamus. Since deep sleep is the state when the brain most effectively records each day's memories in the hippocampus, the burst of a previous fragrance at this time reactivates the same set of neurons that had fired when the fact was first observed by the cortex, the thinking part of the brain.

Other studies claim that memories triggered by a scent are not any more accurate than memories triggered by other stimuli, but they are more emotional. This could be a result of conditioning, where every smell or odour has a personal positive or negative connotation to the individual. For instance, someone who is first exposed to the smell of lilies at a funeral is likely to have negative associations with that smell all her life, whereas the perfume worn by a loved one elicits excitement even on others.

One of the challenges of fragrance research, at least to my mind, is that smell is a difficult variable to control, define and reproduce in the laboratory. Unlike colours that can be defined by a red-blue-green ratio, or sound that can be defined by a pitch-loudness-timbre triplet, scent is still a subjective sense that can best be described by comparison with common everyday smells. That would explain advertisements for room fresheners that evoke clean laundry or green meadows-- borrowing from visual stimuli and depending on cross-association.

If fragrance could be quantified by a cold calculating mathematical number, it would sound the death-knell of the perfume industry-- after all, Calvin Klein could no more patent a smell than Sherwin-Williams can copyright a colour or EMI can register a note. In fact, if you will indulge my cynicism, unlike a painting which is merely a sequence of colour-codes in two-dimensional space, and music which is a linear sequence of notes in time, a smell is a more prosaic presence frozen in the here and now.

AFTERTHOUGHT

Memory--All alone in the moonlight,I can smile at the old days,I was beautiful then.I remember the time I knew what happiness was,Let the memory live again.